The present invention relates to disposable absorbent articles such as diapers, incontinence articles, sanitary towels, training pants and the like, and in particular to articles having a superior liquid handling performance in combination with improved skin aeration, such as improved breathability performance.
Disposable, absorbent articles such as diapers, incontinence articles, sanitary towels, training pants and the like are well known in the art. Typically, disposable absorbent articles comprise a liquid pervious topsheet that faces the wearer""s body, a liquid impervious backsheet that faces the wearer""s clothing, an absorbent core interposed between the liquid previous topsheet and the backsheet, and means to keep the core in fixed relation to the wearer""s body.
In order to receive the body exudates such as urine, faeces or menstrual fluids, the article has to cover certain parts of the wearer""s body. Generally, current articles cover even larger parts of the wearer""s body to allow for adequate storage of the exudates. Whilst this coverage is an essential element of the functionality of the article, the article also canxe2x80x94beyond impacting on the comfort of the wearerxe2x80x94induce negative impact on the skin, such as by exerting pressure on the skin, or by creating occlusion for certain parts of the skin, thereby potentially inducing over-hydration of the skin, in particular under conditions where the wearer has some tendency for sweating.
Numerous attempts have been disclosed aiming at improving on the skin condition of the wearer by allowing the over-hydrated skin to dehydrate to an acceptable level by allowing either air to reach the skin thus minimising potential occlusion effects, and/or by water vapour being removed from the surface of the skin. Generally, such mechanisms are referred to as xe2x80x9cbreathabilityxe2x80x9d or xe2x80x9cvapour or moisture permeabilityxe2x80x9d.
A number of such applications aim at feminine hygiene products, such as catamenial products or so-called xe2x80x9cpanty-linerxe2x80x9d as described in EP-A-0.104.906; EP-A-0.171.041; EP-A-0.710.471. Such products generally have relatively low fluid storage capacity when compared for example to baby diapers or adult incontinence products, often being designed for theoretical capacities significantly exceeding the ones for the feminine hygiene products.
Such breathable materials can be various kinds of webs, such as films which were rendered air/vapour permeable by aperturing as described in U.S. Pat. No. 5,628,737, or by exploiting the xe2x80x9cmicroporosityxe2x80x9d property as described in EP-A-0.238.200; EP-A-0.288.021; EP-A-0.352.802; EP-A-0.515.501; U.S. Pat. No. 4,713,068, whereby small voids are created within the film similar to very small cracks. WO 94/23107; WO 94/28224; U.S. Pat. No. 4,758,239; EP-A-0.315.013 all describe alternative breathable materials which can be fibrous textile or non-woven webs, with air/vapour easily penetrating through the relatively large pores of the structure. Such webs being either treated or untreated with regard to improving their liquid impermeability properties, such as described in EP-A-0.196.654. In WO 95/16562 a laminate of a non-woven with a breathable film is disclosed. Further disclosures such as in WO 95/16746 relate to other materials allowing water molecules to diffuse through. Also, combinations of various materials comprising various layers any of the above elements are also well known.
Generally, all materials exhibit a certain trade off of gas permeability and liquid impermeability. This becomes particularly clear when looking at the pore size of a certain material, whereby an increase will allow easier gas permeation, but also easier liquid permeation. The latter may be undesirable, in particular when such materials are used to cover liquid retaining regions of the article, such as in the core region.
In particular for articles designed for receiving higher amounts of liquids, such as baby or adult incontinence diapers, other approaches were aimed at keeping only part of the article breathable, such as by covering the liquid absorbing parts (often referred to as absorbent core) by a non-breathable material, but having other parts of the article made of breathable materials.
Overall, prior art aimed at improving the breathability of the covering materials, or aimed at keeping only parts of the article breathable at all.
However prior art failed to recognise, that particular benefits can be achieved by selectively combining materials in certain regions of the article, and in particular by exploiting benefits of the absorbency properties of the absorbent core of the article.
The absorbent core of an absorbent article needs to be capable of acquiring, distributing, and storing discharges that are initially deposited on the topsheet of the absorbent article. Preferably the design of the absorbent core is such that the core acquires the discharges substantially immediately after they have been deposited on the topsheet of the absorbent article, with the intention that the discharges do not accumulate on or run off the surface of the topsheet, since this may result in inefficient fluid containment by the absorbent article which may lead to wetting of outer garments and discomfort for the wearer. After the insult, it is an essential functionality of the absorbent article to retain the discharged fluids firmly so as to avoid over-hydration of the skin of the wearer. If the absorbent article is not well functioning in this respect, liquid coming from the absorbent core back to the skinxe2x80x94also often called xe2x80x9crewetxe2x80x9dxe2x80x94can have detrimental effects on the condition of the skin, which can result in overhydration and subsequently a higher propensity for skin irritations.
There have been many attempts to improve the fluid handling properties of absorbent articles or cores, in particular when further requirements were brought up such as a desired reduction of product bulkiness or thickness. Such effects are discussed in European Patent Application 96105023.4 filed on Mar. 29, 1996, but also in U.S. Pat. No. 4,898,642; EP-A-0.640.330; EP-A-0.397.110; EP-A-0.312.118.
So far, however, the approach has been to maintain good skin condition either via aiming at high aeration or by aiming at minimised rewet of the liquid. It has not been sufficiently recognised, however, that there is an interaction between the two mechanisms, thus allowing to exploit both approaches in an improved way, namely by combining products having a very good liquid handling performance resulting in very good skin dryness backsheet materials allowing very good breathability, and in particular by arranging such elements in a novel design providing much improved effect. It has not been realised, that such well performing articles allow much more lenient design of the core covering backsheet materials with regard to liquid permeability, thus allowing even higher air/vapour permeability.
Whilst prior art did place high emphasis on evaluating the liquid handling capability of an absorbent article, such as acquisition or run-off performance, or on the impact the article can have on the wearer""s skin when being in direct contact, such as rewet performance, the relevance of the gas or vapour phase within the article has not been considered sufficiently. In particular in regions where the vapour phase dominates the moisture impact on the skin of a wearer, the vapour moisture has not been recognised sufficiently as an important design parameter for such articles. Also, it is difficult to assess the impact which breathable materials have on the skin condition of the wearer.
Thus it is an object of the present invention to provide disposable absorbent articles having less detrimental effect on the hydration conditions of the wearers skin by allowing better control of the moisture content of the gas volume within an article.
It is a further object, to provide articles, which maintain low vapour phase moisture content through extended wearing and loading situations.
A disposable absorbent article sustaining low vapour phase moisture in the space as enclosed between the article and the wearer in use, such as can be evaluate by measuring relative humidity on a laboratory mannequin, such as can be achieved by combining high performance, low rewet absorbent cores with breathable backsheet materials.